U.S. Pat. No. 4,513,268 entitled "Automated Q-Line Circuit Breaker" describes a fully automated residential-type circuit breaker assembly of the type employing a rotatable operating cradle having its end retained within an armature-latch slot to prevent the circuit breaker operating mechanism from separating the circuit breaker contacts. The latching of the operating cradle within the armature-latch slot is considered a "primary" latch.
U.S. Pat. No. 4,789,848 entitled "Molded Case Circuit Breaker Latch and Operating Mechanism Assembly" describes a latching assembly that includes a primary and a secondary latch. The primary latch is comprised of the operating cradle assembly wherein the secondary latch prevents the cradle from releasing until the secondary latch is first released.
As described within U.S. Pat. No. 4,698,903 entitled "Circuit Breaker High Speed Assembly", a drawback to efficient high speed circuit breaker manufacture is the time-consuming polishing process required on the primary and secondary latching surfaces. The polishing is required to minimize the amount of tripping force that must be applied to overcome the bias of the operating spring and the static friction of the latch surfaces. Although the polishing can be done in a separate pre-assembly process without effecting the actual circuit breaker assembly operation, the trip force required to overcome the operating spring bias and the latch surface friction depends to a certain extent upon the polishing operation. The primary and secondary latch surfaces are fabricated from stamped metal parts which exhibit a rough burr on the edge of one surface and a smooth die roll on the edge of the opposite surface. With secondary latch mating surfaces, the burr edge surface can result in variable frictional forces even after polishing.
An early attempt to reduce friction between the secondary latching surfaces is described within U.S. Pat. No. 4,119,935 entitled "Circuit Interrupter Including Low Friction Latch". This Patent describes latch surfaces having a rough and smooth portion resulting from the metal stamping operation and disposes the secondary latch surface so that only the smooth portion of the latch surfaces are in contact.
U.S. Pat. No. 4,698,903 improves over the earlier described secondary latch assembly within U.S. Pat. No. 4,119,935 by orienting the secondary latch surfaces so that the smooth die roll edges are in contact and further reduces the friction between the primary latch surfaces by a shaving operation applied to the end of the cradle to further reduce the friction encountered between the end of the cradle and the latch surface. The shaving operation is described within the publication entitled "Advanced Die Making", McGraw Hill Book Company, 1967 edition, New York, New York.
In an attempt to reduce the primary latch friction, without requiring either polishing or shaving during the circuit breaker assembly operation, a highly polished shim insert was positioned within the armature-latch arrangement in an off-line assembly described in the aforementioned U.S. Pat. No. 4,513,268. The insert was in the form of a highly polished stainless steel shim that was welded or brazed within the cradle retaining slot formed in the armature-latch component. It would be economically advantageous to eliminate the on-line shaving process and to eliminate the off-line polished shim insert without effecting the circuit breaker trip response.
It is accordingly one purpose of the invention to substantially reduce the static friction existing between the primary latch surfaces without requiring any shaving or shim insertion operations whatsoever.